The invention relates to the field of modern medical biology. In particular the invention relates to stem cell technology. More in particular the invention relates to stem cell technology, in particular postembryonic stem cell technology.
Stem cells are primal undifferentiated cells which have the ability for self-renewal and the ability to differentiate into other cell types. This ability allows them to act as a repair system for the body, replenishing other cells as long as the organism is alive.
Stem cells are categorized by potency which describes the specificity of that cell.
Totipotent stem cells are cells that have the ability of self renewal and are capable of differentiating into any and all cell type to form an entire new organism. They are typically produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg cell are also totipotent. These cells can grow into any cell type without exception.
Pluripotent stem cells are the descendants of totipotent cells and can grow into any cell type except for totipotent stem cells.
Multipotent stem cells can produce only cells of a closely related family of cells (e.g. hematopoietic stem cells can differentiate into blood cells such as red blood cells, white blood cells and platelets).
Unipotent cells (sometimes called progenitor cells) can produce only one cell type; but, have the property of self-renewal which distinguishes them from non-stem cells.
Stem cells are also categorized according to their source, as either adult (postembryonic) or embryonic stem cells.
Adult stem cells are undifferentiated cells found among differentiated cells of a specific tissue and are mostly multipotent cells. They are more accurately called somatic stem cells, because they need not come from adults but can also come from children or umbilical cords.
Embryonic stem cells are cells obtained from the undifferentiated inner mass cells of a blastocyst, an early stage embryo that is 50 to 150 cells.
Blood from the placenta and umbilical cord that are left over after birth is one source of adult stem cells. It is collected by removing the umbilical cord, cleansing it and withdrawing blood from the umbilical vein. Other sources are bone marrow (BM) or G-CSF-mobilized peripheral blood (mPB)
Red blood cells and platelets can be removed from the cord blood, BM or in PB and the remaining cells containing the stem cells can be used or stored (e.g. in liquid nitrogen).
Stem cells themselves are useful in many applications of so-called regenerative medicine. They have been used to treat heart disease, repair spinal cords and many other diseases where tissues of all kinds needed to be replaced.
Stem cells can also be used to produce certain kinds of differentiated cells that are effector cells in certain diseases.
Unfortunately however, stem cells are present in the body of a mammal in small quantities only. Often they are present in organs or tissues that can not easily be reached. Embryonic stem cell are also not easily obtainable and only in minute quantities. Moreover, there are some ethical concerns in growing embryos merely for the purpose of producing stem cells. There is a need therefore for methods for multiplying available stem cells and/or primitive lineage specific progeny thereof, without differentiating into less potent descendants. Totipotent stem cells should remain totipotent after expansion and not turn into pluripotent stem cells, pluripotent stem cells should remain pluripotent, etc. In some instances the change into a less potent descendant may be acceptable (at least to a certain extent) as long as the potential for self renewal and at least multipotency is retained.